*{
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  word-wrap: break-word;
  font-family: '微软雅黑', sans-serif;
}

body{
  background: #000;
  min-height: 200vh;
}
header{
  position: fixed;
  top:0;
  left: 0;
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  transition: 0.6s;
  padding: 40px 100px;
  z-index: 2;
}

header.sticky{
  padding: 5px 100px;
  background: #fff;
}

header .logo{
  position: relative;
  font-weight: 700;
  color: #fff;
  text-decoration: none;
  font-size:2em;
  text-transform: uppercase;
  letter-spacing: 2px;
  transition: 0;
}

header ul{
  position: relative;
  display: flex;
  justify-content: center;
  align-items: center;
}

header ul li{
  position: relative;
  list-style: none;
}

header ul li a{
  position: relative;
  margin: 0 15px;
  text-decoration: none;
  color: #fff;
  letter-spacing: 2px;
  font-weight: 500px;
  transition: 0.5s;
}


.banner{
  position: relative;
  width: 100%;
  height: 100vh;
  background: url(bg.jpg);
  background-size: cover;
}
header.sticky .logo,
header.sticky ul li a{
  color: #000;
}